From 1e65b8ad5967d41dc56d7dce015f4bb6c1af26dd Mon Sep 17 00:00:00 2001
From: Hao Huang <hhuang@driver.xyz>
Date: Fri, 10 Feb 2017 16:17:01 -0800
Subject: Add the companion ordering object for Date

---
 src/main/scala/xyz/driver/core/date.scala     | 10 +++++++
 src/test/scala/xyz/driver/core/DateTest.scala | 41 +++++++++++++++++++++++++++
 2 files changed, 51 insertions(+)
 create mode 100644 src/test/scala/xyz/driver/core/DateTest.scala

diff --git a/src/main/scala/xyz/driver/core/date.scala b/src/main/scala/xyz/driver/core/date.scala
index bb88501..f0b9bf6 100644
--- a/src/main/scala/xyz/driver/core/date.scala
+++ b/src/main/scala/xyz/driver/core/date.scala
@@ -26,6 +26,16 @@ object date {
   }
 
   object Date {
+    implicit def dateOrdering: Ordering[Date] = Ordering.fromLessThan { (date1, date2) =>
+      if (date1.year != date2.year) {
+        date1.year < date2.year
+      } else if (date1.month != date2.month) {
+        date1.month < date2.month
+      } else {
+        date1.day < date2.day
+      }
+    }
+
     def fromString(dateString: String): Option[Date] = {
       util.Try(dateString.split("-").map(_.toInt)).toOption collect {
         case Array(year, month, day) if (1 to 12 contains month) && (1 to 31 contains day) =>
diff --git a/src/test/scala/xyz/driver/core/DateTest.scala b/src/test/scala/xyz/driver/core/DateTest.scala
new file mode 100644
index 0000000..50f8521
--- /dev/null
+++ b/src/test/scala/xyz/driver/core/DateTest.scala
@@ -0,0 +1,41 @@
+package xyz.driver.core
+
+import org.scalacheck.{Arbitrary, Gen}
+import org.scalatest.prop.Checkers
+import org.scalatest.{FlatSpec, Matchers}
+import xyz.driver.core.date.Date
+
+class DateTest extends FlatSpec with Matchers with Checkers {
+  val dateGenerator = for {
+    year  <- Gen.choose(0, 3000)
+    month <- Gen.choose(0, 11)
+    day   <- Gen.choose(1, 31)
+  } yield Date(year, date.tagMonth(month), day)
+  implicit val arbitraryDate = Arbitrary[Date](dateGenerator)
+
+  it should "have ordering defined correctly" in {
+    Seq(Date.fromString("2013-05-10"),
+        Date.fromString("2020-02-15"),
+        Date.fromString("2017-03-05"),
+        Date.fromString("2013-05-12")).sorted should
+      contain theSameElementsInOrderAs Seq(Date.fromString("2013-05-10"),
+                                           Date.fromString("2013-05-12"),
+                                           Date.fromString("2017-03-05"),
+                                           Date.fromString("2020-02-15"))
+
+    check { dates: List[Date] =>
+      dates.sorted.sliding(2).filter(_.size == 2).forall {
+        case Seq(a, b) =>
+          if (a.year == b.year) {
+            if (a.month == b.month) {
+              a.day < b.day
+            } else {
+              a.month < b.month
+            }
+          } else {
+            a.year < b.year
+          }
+      }
+    }
+  }
+}
-- 
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